how do you make actor's voices more real and life-like?

The voices you can download and install for Captivate are better than the default Microsoft voices that are listed, but they're still 'robotic'.

With some creative editing of the text, you can make pronunciations a little more clear (i.e. liberal use of commas or periods, phonetic spelling) but the overall quality is only as good as the voice itself.

This post may help with some options:

Text-to-Speech in Captivate 8 | eLearning Chef

However, it's not easy to install new voices. A lot of TTS voices require their own application...which may be worth it since a lot ARE quite good (i.e. Loquendo/Nuance)...but they're also not cheap.

So overall, there's no easy solution for your issue...other than using real people